Applescript support was added back to Numbers 3.1 after being removed in Numbers '13. As long as you have '09 or 3.1, Applescript support would not be a problem.
It sounds like you're trying to write the application as a layer over a running version of Numbers/Excel, and not really as a standalone application. In that case, it sounds like your best bet may be using VBA for Mac with Excel. I'm not very familiar with VBA, but this Stack Overflow question has some example code for making a custom toolbar, and this forum has example socket code. VBA also allows you to create Macros for working with sheets, cells, and ranges.
If you want a standalone app, you could split the domains into separate languages. Use Objective-C/Bash/Python for the socket stuff, Applescript for manipulating spreadsheets, and VBA for GUI elements.